In leaded semiconductor chip packages, a chip is generally affixed to a paddle on a leadframe using a permanent adhesive. In some cases, it is desirable to enhance the thermal performance of a package by improving the path for the departure of heat from the chip through the leadframe. In many such cases, it is known to attach a heat spreader to the surface of the paddle opposite the chip, such as by welding, taping, or gluing. In other cases, the leadframe paddle is dispensed with, using instead a heat spreader riveted in place on the leadframe. The chip is then mounted directly to the heat spreader surface. In either case, due to its heat conduction properties, the heat spreader is typically made from metal, such as copper or copper alloy. Generally, in order to increase its heat conduction, the heat spreader is large relative to the chip, extending in a plane parallel with the proximal ends of the leadfingers. The leadframe is typically planar, with leadfingers extending in a straight path from the edges toward the chip location. This type of arrangement of chip, leadfingers, and heat spreader at least partially underlying the leadfingers, is used in many applications, but is not without its problems.
Electrical connections within a semiconductor chip package are commonly made by bonding wires from bond pads on the exposed surface of the chip to the leadfingers. The leadfingers typically extend in a straight line from one end adjacent to a gap in the leadframe proximal to the chip, to a distal end at the exterior of the package where electrical connections may be made to the outside world. During a typical wirebonding process, a ball bond is formed on a bond pad of the chip using heat, pressure, and in many cases ultrasonic vibrations. The wire is then pulled to the appropriate proximal end of a leadfinger, and a stitch bond is formed there, also using some combination of heat and pressure, and often ultrasonic vibrations.
In package assemblies having a heat spreader extending parallel to the proximal ends of the leadfingers, it is often impractical to support the leadfingers during wirebonding. In some applications, where support to leadfingers during wirebonding is deficient, it is known to provide increased clearance between the leadfingers and the underlying heat spreader by increasing the distance between them, or by downsetting the chip pad away from the plane of the leadfingers. The result in such cases is thicker package assemblies, which in most applications is undesirable. On the other hand, minimizing thickness by reducing such clearance can result in electrical problems and defective package assemblies.
Due to these and other technological problems, improved leadfingers, leadframes, semiconductor chip package assemblies, and methods for their manufacture would provide useful and advantageous contributions to the art. The present invention is directed to overcoming, or at least reducing, problems present in the prior art, and contributes one or more heretofore unforeseen advantages indicated herein.